Systems and methods for an electronic hook switch for customer premises equipment

ABSTRACT

Embodiments of the present invention relate to systems and methods for an electronic hook switch for customer premises equipment. In an embodiment, a system includes a first lead configured to be coupled to a tip wire and a second lead and the second lead to a ring wire. A diode bridge is coupled to the first lead and the second lead had a positive output. A low side switch is coupled to the positive output of the diode bridge without a high side switch between the low side switch and the positive output of the diode bridge.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.10/400,648, filed Mar. 28, 2003, now U.S. Pat. No. 7,103,175 whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/438,532 filed Jan. 8, 2003, which are both incorporated herein byreference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to customer premisesequipment. More particularly, embodiments of the present inventionrelate to systems and methods for an electronic hook switch for customerpremises equipment.

2. Background Information

While telephone infrastructure varies from country to country, theUnited States infrastructure provides a useful starting point forpurposes of describing background information and embodiments of thepresent invention. Naturally, the embodiments described herein areuseful in other contexts. In the United States, a landline phone can bea cordless or corded telephone that is coupled to a central office(“CO”) of a local exchange carrier (“LEC”) such as a Regional BellOperating Company (“RBOC”), a competitive local exchange carrier(“CLEC”), and so on. Cordless telephones have no cord between thehandset and base, each of which have a radio transmitter, receiver andantenna for communications between the handset and base. Typically, thehandset includes a rechargeable battery, and the base is powered bycurrent from an alternating current (“AC”) outlet (e.g., of a house,office, etc.). The range of effective communications between the handsetand base can be from 10 feet to several miles depending on factors suchas product design, operating radio frequency(s), environmentalconditions, and legal restrictions (e.g., laws, regulations, etc.).Examples of known operating radio frequencies for cordless telephonecommunications in the United States include 900 Megahertz (“MHz”), 2.4Gigahertz (“GHz”), 5.8 GHz, a combination thereof, and so on.

In a residential environment, the base is typically coupled to the COvia one or more wires, such as an RJ-11 wire that couples the base to anRJ-11 jack on a wall or in a floor. The RJ-11 jack is typically coupledto the CO via a twisted-pair wire. The CO can provide voltage andcurrent to a telephone coupled to the CO via the RJ-11 wire and theRJ-11 jack. For example, known corded phones draw power from the COduring telephone call dialing and during the telephone call. Each RJ-11jack usually has four wires, which consist of two sets of a tip and ringpair. A single-line corded phone is typically coupled to one set of atip and ring pair (and can draw power from that tip and ring pair), anda two-line corded phone is typically coupled to each of the two sets ofthe tip and ring pairs (and can draw power from either or both tip andring pair).

As used to describe the background and embodiments of the presentinvention, the term “coupled” encompasses a direct connection, anindirect connection, or a combination thereof. Two devices that arecoupled can engage in direct communications, in indirect communications,or a combination thereof. Moreover, two devices that are coupled neednot be in continuous communication, but can be in communicationtypically, periodically, intermittently, sporadically, occasionally, andso on. Further, the term “communication” is not limited to directcommunication, but also includes indirect communication.

Cordless phones typically do not draw power from the tip and ring pairsbecause the cordless phone base is powered by current from an AC outlet.Cordless phones, however, are still connected to one or more of the tipand ring pairs to transmit and receive voice and data communicationsignals. Moreover, a cordless phone base includes electronic circuitrythat is powered at a relatively low voltage as compared to the voltagesassociated with a tip and ring pair. For example, electronic circuitryis often powered at 12 volts, 5 volts, 3.3 volts, and so on. Incontrast, voltages associated with a tip and ring pair can be as high as350 volts.

In known telephones, an electronic hook switch consists of a high sideswitch and a low side switch, so that a low voltage control integratedcircuit (“IC”) (e.g., a microcomputer unit, a dialer IC, a specificcontroller, etc.) can control the electronic hook switch notwithstandingthe high voltage between tip and ring. In such known systems, whether ornot they are constructed using bipolar transistors or MOSFETs, neitherthe high side switch nor the low side switch is omitted. Because thesesystems have both a high side switch and low side switch, there aredisadvantageous cost and system design implications.

For example, known customer premises equipment (“CPE”), such as atelephone, usually employs two Darlington connected PNP transistors tobuild the high side switch and have one NPN transistor for the low sideswitch. If P-channel MOSFET is used for the high side switch, anN-channel MOSFET is required for the low side switch to translate theline voltage level to a voltage low enough to interface with the controlcircuit. Often, each of the low side switch and the high side switchhave to withstand voltages as high as 350 volts. In view of theforegoing, it can be appreciated that a substantial need exists forsystems and methods that can advantageously provide for an electronichook switch for customer premises equipment.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention relate to systems and methods foran electronic hook switch for customer premises equipment. In anembodiment, a system includes a first lead configured to be coupled to atip wire and a second lead configured to be coupled to a ring wire. Adiode bridge is coupled to the first lead and the second lead and has apositive output. A low side switch is coupled to the positive output ofthe diode bridge without a high side switch between the low side switchand the positive output of the diode bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a known telephone line interface circuit.

FIG. 2 is a system diagram of a telephone line interface circuit inaccordance with an embodiment of the present invention.

FIG. 3 shows an example of a known telephone interface circuit design.

FIG. 4 is a system diagram of a telephone interface circuit design inaccordance with an embodiment of the present invention.

Before one or more embodiments of the invention are described in detail,one skilled in the art will appreciate that the invention is not limitedin its application to the details of construction, the arrangements ofcomponents, and the arrangement of steps set forth in the followingdetailed description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or being carried outin various ways. Also, it is to be understood that the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting.

DETAILED DESCRIPTION OF THE INVENTION

According to an embodiment of the present invention, a telephone systemincludes a telephone line interface circuit that avoids the use of thehigh side switch in an electronic hook switch circuit. The electronichook switch can then consist of an NPN transistor or N-channel MOSFET.As a result, space and cost is saved. Because a telephone line interfacecircuit can be constructed with fewer components, a printed circuitboard (“PCB”) or integrated circuit including the electronic hook switchcan be of reduced size. Thus, a telephone system (e.g., a cordlesstelephone base) can be produced and sold at a lower price.

FIG. 1 shows the block diagram of an example of a known telephone lineinterface circuit 100. Telephone network 10 is connected to tip 101 andring 102. Protection circuit 103 avoids over voltage damage to thesubsequent circuit and diode bridge 104 regulates the line DC voltage toa fix polarity for the remainder of the telephone line interface circuit100. If the Microcomputer Unit (MCU) 106 drives the low side switch 105to on, current ID1 119 will flow and turn on the high side switch 117.Then the loop is closed and the loop current will pass through the highside switch 117 and the circuitry behind it. This status is usuallycalled an off-hook condition. In contrast to this off-hook status, ifthe MCU 106 drives the low side switch 105 to off, current ID1 119 willno longer flow and the high side switch 117 will be off. As a result,the loop is open and no loop current will flow into the circuitry behindthe high side switch 117. This known telephone interface circuit 100 andits operations are representative of how a typical known electronic hookswitch is constructed and operates.

The open loop voltage on the line can be as high as 350 volts. The MCU106 cannot directly drive the high side switch 117 because it is lowvoltage device and cannot withstand a voltage as high as 350 volts.While it is in an off-hook condition, the signal coming in will beextracted by the passive side tone network 118 and amplified by the linein amplifier 112. Outgoing signal is amplified by the line out amplifier111 and fed into the line through the line driven amplifier 107. Withrespect to the flow of the loop current, it passes through the high sideswitch 117 and the line driven amplifier 107 and back to the telephonenetwork 10. Circuit elements such as the line in amplifier 112, line outamplifier 111 and the MCU 106 typically need an auxiliary power supply.In some known systems, these circuit elements draw power directly fromthe telephone network 10, as in the case in a typical corded phone.Usually, no matter where the power comes from, the power supply circuit113 will have the same reference ground 121 as the MCU 106, the low sideswitch 105 and the amplifier circuit elements 111, 112, and 107. This isusually required to use an auxiliary power supply and set up a normalsignal path. Typically, the reference ground 121 of the telephone lineinterface circuit 100 is at the negative output of the diode bridge 104.

FIG. 2 is a system diagram of a telephone line interface circuit inaccordance with an embodiment of the present invention. In an embodimentof the present invention, an improved telephone line interface circuit200 does not include the high side switch present in known telephoneline interface circuits. For example, telephone line interface circuit200, as compared to the known telephone line interface circuit 100,includes all the circuit elements of telephone line interface circuit100 except the high side switch 117. Moreover, in an embodiment, theinterconnections between the circuit elements of telephone lineinterface circuit 200 remain substantially the same as theinterconnections between the circuit elements of known telephone lineinterface circuit 100. Furthermore, in an embodiment, each of thecircuit elements of circuit 200 can have same internal design as thecorresponding circuit elements in know circuit 100. According to anembodiment of the present invention, the only changes reflected incircuit 200 as compared to known circuit 100 is that the low side switch105 is coupled to the positive output of the diode bridge 104, and theline driven amplifier 107 is coupled to the negative output of the diodebridge 104. Also, the reference ground 121 is not at the negative outputof the diode bridge. In telephone line interface circuit 200, the loopcurrent passes through the low side switch 105 and the line drivenamplifier 107 and back to the telephone network 10 in an off-hook state.In an embodiment, the line driven amplifier is biased by a negativevoltage, which can be accomplished a variety of ways. By way of example,for a bipolar solution, the NPN transistor is changed to PNP transistoror vice-versa. The AC signal is coupled by capacitors 109, 110. Thevoltage across these capacitors 109, 110 can increase a few voltsbecause they now block the DC biasing between the negative voltageoperated circuit elements 107, 108 and the positive voltage operatedcircuit elements 106, 111, and 112. In other embodiments of the presentinvention, however, a low voltage capacitor still can be used.

FIG. 3 shows an example of a known telephone interface circuit design300. The high side switch is formed by the transistors 304 and 308. Thelow side switch is formed by transistor 310, and the line drivenamplifier is formed by transistors 301 and 307. One skilled in the artwill appreciate that the current that drives the high side switch ispart of the loop current, and that current cannot be set too highotherwise the off-hook DC V-I characteristic may be violated. Thecurrent, however, must be large enough to drive the high side switchinto saturation. An undesirable condition occurs when the voltagebetween tip and ring is very low, which can be caused by a parallelphone. Thus, known circuits use a low driven current and a high gaintransistor to construct the high side switch. Unfortunately, a highvoltage PNP transistor usually has low current gain. As a result, twoPNP transistors in Darlington configuration are typically employed toform the switch with enough current gain.

FIG. 4 is a system diagram of a telephone interface circuit design 400in accordance with an embodiment of the present invention. As comparedto known circuit design 300, circuit design 400 lacks the two highvoltage PNP transistors (i.e., transistors 304, 308) and high voltageNPN transistor 410 acts as the low side switch. One skilled in the artwill appreciate that the current driving transistor 410 is not part ofthe loop current, but rather comes from the MCU 406 and thus is from theauxiliary power supply. In an embodiment, this is advantageous becausethe magnitude of the driving current does not affect the DC V-Icharacteristic, provided that the driving current is high enough todrive the transistor to saturation. Thus, in an embodiment, a highdriving current can drive the switch without concerning violating theoff-hook DC V-I characteristic and only one NPN transistor is used inthe low side switch.

In the above example of circuit design 400, as compared to known circuitdesign 300, two high voltage PNP transistor are not used and therebyfrom a manufacturing and cost standpoint are “saved.” Embodiments of thepresent invention, such as circuit design 400, have demonstrated thatthere is little or no impact on the high voltage protection circuit andthe whole design passes the UL and FCC part 68 tests.

Embodiments of the present invention encompass not only telephones butalso other Customer Premises Equipment (CPE) that is coupled to thetelephone network, such as, but not limited to, answering machines, faxmachines, computer modems, and so on. Embodiment of the presentinvention can be implemented in these CPE and can help reduce productioncosts. For example, in the example of an integrated circuit thatincludes a telephone line interface circuit, embodiments of the presentinvention can reduce chip size and thus the cost of the chip.

Embodiments of systems and methods for an electronic hook switch forcustomer premises equipment have been described. In the foregoingdescription, for purposes of explanation, numerous specific details areset forth to provide a thorough understanding of the present invention.It will be appreciated, however, by one skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, structures and devices are shown in block diagram form.Furthermore, one skilled in the art can readily appreciate that thespecific sequences in which methods are presented and performed areillustrative and it is contemplated that the sequences can be varied andstill remain within the spirit and scope of the present invention.

In the foregoing detailed description, systems and methods in accordancewith embodiments of the present invention have been described withreference to specific exemplary embodiments. Accordingly, the presentspecification and figures are to be regarded as illustrative rather thanrestrictive. The scope of the invention is to be defined by the claimsappended hereto, and by their equivalents.

What is claimed is:
 1. A system for an electronic hook switch forcustomer premises equipment, comprising: a first lead configured to becoupled to a tip wire; a second lead configured to be coupled to a ringwire; a diode bridge coupled to the first lead and the second lead,wherein the diode bridge has a positive output and a negative output; alow side switch directly coupled to the positive output of the diodebridge; and a line driven amplifier coupled to the negative output ofthe diode bridge.
 2. The system of claim 1, wherein one side of the lowside switch is directly coupled to the positive output of the diodebridge and the other side of the low side switch is coupled to ground,and wherein the reference ground is not at the negative output of thediode bridge.
 3. The system of claim 1, wherein the first lead and thesecond lead are coupled to a protection circuit.
 4. The system of claim1, wherein the low side switch includes a high voltage PNP transistor.5. The system of claim 1, wherein a current driving the low side switchis coming from an auxiliary power supply.
 6. The system of claim 1,further comprising a MCU (Microcomputer Unit) coupled with the low sideswitch, the MCU provides a current to drive the low side switch to besaturated in an off-hook situation.
 7. The system of claim 6, whereinthe MCU is coupled to an auxiliary power supply.
 8. The system of claim1, further comprising a sidetone network coupled to the negative outputof the diode bridge.
 9. The system of claim 8, wherein the sidetonenetwork is further coupled to the line driven amplifier.
 10. A systemfor an electronic hook switch for customer premises equipment, thesystem comprising: a protection circuit coupled with a first lead and asecond lead of the electronic hook switch, wherein the first lead isconfigured to be coupled to a tip wire of the electronic hook switch andthe second lead is configured to be coupled to a ring wire of theelectronic hook switch; a diode bridge coupled to the protectioncircuit, the diode bridge comprises a positive output and a negativeoutput; a low side switch directly coupled to the positive output of thediode bridge; a line driven amplifier directly coupled to the negativeoutput of the diode bridge; and a sidetone network coupled to thenegative output of the diode bridge through the line driven amplifier.11. The system of claim 10, wherein the sidetone network is furthercoupled to the line driven amplifier.
 12. The system of claim 10,wherein the low side switch is further coupled to a reference ground,and wherein the reference ground is not at the negative output of thediode bridge.
 13. The system of claim 10, further comprising a MCU(Microcomputer Unit) coupled to the low side switch, the MCU provides acurrent to drive the low side switch to be saturated in an off-hooksituation.
 14. The system of claim 13, wherein the MCU is coupled to anauxiliary power supply.
 15. The system of claim 10, wherein the low sideswitch includes a high voltage PNP transistor.
 16. A system for anelectronic hook switch for customer premises equipment, the systemcomprising: a protection circuit coupled with a first lead and a secondlead of the electronic hook switch, wherein the first lead is configuredto be coupled to a tip wire and the second lead is configured to becoupled to a ring wire of the electronic hook switch, respectively; adiode bridge coupled to the protection circuit, the diode bridgecomprises a positive output and a negative output; a low side switchdirectly coupled to the positive output of the diode bridge on one endand ground on the other end; a microcomputer unit (MCU) coupled to thelow side switch, the MCU provides current to the low side switch todrive the low side switch to be saturated in an off-hook situation; aline driven amplifier directly coupled to the negative output of thediode bridge; and a sidetone network having an input port coupled to thenegative output of the diode bridge and an output port coupled to theline driven amplifier.
 17. The system of claim 16, wherein the MCU iscoupled to an auxiliary power supply.
 18. The system of claim 17,wherein the current driving the low side switch to be saturated is fromthe auxiliary power supply.
 19. The system of claim 17, wherein the lowside switch includes a high voltage PNP transistor.